Hydrashift DB 1412 won't shift to 2'nd

[db1410]

Hi guys,

Trouble with hydra-shift gearbox from David Brown 1412

Before last week Hydra-shift box was great.
Now, at low engine speed, gearbox won't shift from 1'st to 2'nd
shift from 2'nd to 3'th is good and shift from 3'th to 4'th is also great. When engine at high speed, gearbox will shift fro 1'st to 2'nd but with a delay of more than 30seconds.

I allready tested the pump relief valve:
1'st: 73psi
2'nd: 72psi
3'th: 75psi
4'th: 77psi
When I checked the workshop manual: pressures are correct.

Gage pressure when shifting from 1'st to 2'nd:
pressure drops from 73psi to lower pressure for a long time, when higher revolution speed, pressure rises to 72 psi.

My opinion is that there's no excessive leakage at front clutch unit cause shift from 3'th to 4'th is good.

Does anyone had this problem in the past?
Could it be a problem with the front sequence valve?

Many thanks if you could help to resolve this problem.

[ollek]

There can still be a leak at the front clutch, because the pump output in bigger in gear 3 than in gear 1 (higher speed at pump).

[jimc1390]

the preasure is definetly going somewhere, with plenty of revs on is it shifting fine? if you leave it in second and shut the revs righ back will it slip back to first?
i'm not sure its sequence valve as this would still play up in 4th, the sequence valve is just there to make sure the brake band is released boefore the clutch pack is locked up for solid drive, id probably try and run it in second with plenty of revs on, drop the revs right off watching the presure guage to see at what point it slips out, its a strange one although my gut reaction that if its in 4th ok the front pack must be fine in reality there must be a leak there somewhere

[DB780]

I agree with Jim, you have a leak in the front clutch or the pipework going to it. If you cannot engage 2nd then you should not be able to get a true 4th because in 4th both clutches are locked. I don't think it's a good idea to run the tractor any longer than you need to because you could be causing unnecessary damage to the clutch unit.

Ollek's theory about the pump running faster in 3rd gear is not correct. Pump speed is governed by engine speed not which range gear is selected.

[db1410]

Hi,

thank you for helping.
Next week, I'll search the problem.
Here a picture of the DB1412